Moulding compound, use thereof and a method for producing an oxide-ceramic sintered body

ABSTRACT

The invention proposes to produce a mixture that is shrink-resistant, or has a freely selectable degree of shrinkage, and can be used as a molding compound, and a method for producing a corresponding oxide-ceramic sintered body. The molding compound comprises an intermetallic compound and a wax. In the method for producing an oxide-ceramic sintered body, a green body is molded from a molding compound of this type, dewaxed and sintered in an oxidizing atmosphere to form a ceramic sintered body. The molding compound is suited for producing dentures and dental fillings.

[0001] The invention relates to a molding compound according to thefirst claim, its use according to claims 7 and 8, and a method forproducing an oxide-ceramic sintered body according to claim 6.

[0002] DE 195 47 129 C1 discloses a mixture and a method for producingshrink-resistant ceramics. The mixture described here comprises apowdered oxide ceramic, a powdered, intermetallic compound and anorganosilicon polymer. This mixture forms a green body that can besintered in an oxidizing atmosphere without shrinking.

[0003] It is the object of the invention to modify the known mixturesuch that it performs better as a molding compound, particularly alow-pressure injection-molding compound. The invention further proposesa method for producing a shrink-resistant sintered body and a possibleapplication for the molding compound.

[0004] The object is accomplished by the molding compound described inclaim 1 and the method disclosed in claim 6. Claims 7 and 8 relate tothe use of the molding compounds. The remaining claims describepreferred embodiments of the molding compound.

[0005] According to the invention, the organosilicon polymer proposed inthe cited DE 195 47 129 C1 is replaced, completely or partially, with awax, preferably a paraffin. As in the known mixture, an oxide ceramicmay be present as a third component, in addition to the intermetalliccompound and the wax; oxide-ceramic sintered bodies can, however, beproduced only from the intermetallic compound and the wax.

[0006] The following definition of waxes can be found in the CD-ROMversion 1.0 of the Römpp Chemie Lexikon [Chemical Lexicon],Stuttgart/New York, Georg Thieme Verlag [publisher], 1995. Basically,all of the waxes that fall under this definition and are listed here aresuitable for producing the molding compounds; paraffins are alsoparticularly well suited, however.

[0007] If the molding compound is to be sintered into a highly stableoxide ceramic, a high sintering density, preferably more than 95% of thetheoretically attainable density, is required. For this purpose, twoprerequisites must be met:

[0008] (i) A high filler content in the molding compound. This isattained through a surface modification of the intermetallic phase,particularly with a silane jacket.

[0009] (ii) A high sintering density. This can be attained through theaddition of auxiliary sintering agents, such as inorganic alkali oralkaline-earth compounds such as Li₂O.

[0010] The composition of the molding compound, i.e., the components ofintermetallic phase, wax and possibly oxide ceramic, are selected inaccordance with the above-cited DE 195 47 129 C1 such that the sinteringshrinkage of the body sintered into an oxide ceramic in an oxidizingatmosphere can either be minimized or set at a predetermined value.Thus, shrink-free sintered bodies or bodies having a selected shrinkagecan be produced from the molding compound.

[0011] In contrast to the molding compound from the cited DE 195 47 129C1, the molding compound of the invention has the notable advantage thatwaxes, particularly paraffins, are considerably less expensive thanorganosilicon polymers. Moreover, they possess the followingadvantageous features:

[0012] the option of completely omitting the oxide ceramic;

[0013] improved handling;

[0014] a lower processing temperature (from ambient temperature to about80° C.);

[0015] a high filling component of the intermetallic phase;

[0016] the ability to be poured or sprayed without solvents; and

[0017] the ability to be used in an impression method to produceprecisely detailed replicates.

[0018] The molding compound can be used to produce high-quality greenbodies, through injection molding, particularly low-pressure injectionmolding, through second casting or through replication, wax molding orother known molding methods. Such bodies cannot be produced with theknown mixture and the known method.

[0019] In the method of the invention, after the green body has beenproduced at temperatures of, for example, 40° C. to 200° C., the wax ismelted out; the liquid wax can be collected and reused, if necessary.The high filler content that can be achieved, for example, by thesilanization of the intermetallic phase allows an especially tightinterlocking of the powder particles, so the dewaxed green body retainsits original shape.

[0020] After the dewaxing process, the green bodies are sintered in aknown manner in an oxidizing (oxygen-containing) atmosphere, withoutshrinking, to form oxide-ceramic bodies. The maximum sinteringtemperatures used in the heating process in the oxidizing atmosphere canbe between 1000° C. and 1650° C.

[0021] Because the molding compound and the method can attain an exactreproduction, the molding compound is particularly suited for use indentistry, for example for dentures and ceramic dental fillings.

[0022] The invention is described in further detail below by way of twoexamples. In both instances, the produced ceramic components virtuallycannot be distinguished from the green body in dimension, and are thussintered without shrinkage.

EXAMPLE 1

[0023] 75.42 g of zirconium silicide are attrition-ground for two hoursin ethanol. Afterward, 74.58 g of tetragonally stabilized zirconiumdioxide are added, and the mixture is ground and mixed for an hour inthe attritor. The powdered mixture is dried in a vacuum, then left in adrying oven for two hours at 120° C.

[0024] 9.666 g of paraffin and 1.568 g of PEG(2)stearylether (PEG:Polyethylene glycol) are melted at 80° C. Then, 100 g of the preparedpowdered mixture are stirred into this wax mixture, and homogenized at90° C. for three hours.

[0025] The resulting compound can easily be molded in silicon moldswithout bubbles at 120° C. The unmolded green bodies are releasedwithout cracks at 500° C., and the attained brown bodies aredense-sintered at 1550° C. to form the finished component.

EXAMPLE 2

[0026] The powdered mixture prepared as in Example 1 is pretreated toform a hot-pour compound prior to being processed.

[0027] To this end, 285 ml of ethanol are mixed with 15 ml of deionizedwater and 3 ml of acetic acid and stirred. Then, 5.59 g ofn-octyltriethoxysilane are added. Afterward, 100 g of the powderedmixture prepared as in Example 1 are added to the clear solution, andheld in suspension for 30 minutes. The powder is, again, dried in avacuum and left in a drying oven for two hours at 120° C. There-processing to form a hot-pour molding compound, as in Example 1,follows.

1. A molding compound comprising a) an intermetallic compound and b) awax.
 2. The molding compound according to claim 1, having an oxideceramic as an additional component.
 3. The molding compound according toclaim 1 or 2, with the addition of Li₂O as a sintering aid.
 4. Themolding compound according to claim 1, 2 or 3, in which the surface ofthe intermetallic compound is coated with a silane.
 5. The moldingcompound according to one of claims 1 through 4, with paraffin as thewax.
 6. A method for producing an oxide-ceramic sintered body, in whicha) a homogeneous mixture is produced from a powdered, intermetalliccompound and a wax; b) a green body is molded from the homogeneousmixture; c) the green body is dewaxed; and d) the green body is sinteredin an oxidizing atmosphere to form a ceramic sintered body.
 7. The useof the molding compound according to one of claims 1 through 4 toproduce dentures.
 8. The use of the molding compound according to one ofclaims 1 through 4 to produce a dental filling.